Method and medium for electron beam recording



R. F. DUBBE ETAL METHOD AND MEDIUM FOR ELECTRON BEAM RECORDING Filed Dec. 28, 1964 INVENTORS P/CH/QPD 00555 PQUL FPA'M r4776 NE 5 United States Patent 3,331,076 METHOD AND MEDIUM FOR ELECTRON BEAM RECORDING Richard F. Duhhe, Richfield, and Paul Fran], Lincoln Township, Washington County, Minn., asslgnors to Minnesota Mining and Manufacturing Company, St. Paul, Minn., a corporation of Delaware Filed Dec. 28, 1964, Ser. No. 421,328 Claims. (Cl. 346-1) This invention relates to a new and very useful storage medium suitable for direct electron beam recording and subsequent direct optical readout which employs an electron sensitive layer as its information storage component and which employs an organic polymeric film forming binder which becomes water soluble when treated with mild alkali solution and which is electrically conductive because of electrically conductive, finely divided particles dispersed therein which layer serves as a means to dis. sipate electrons during a direct electron beam recordmg operation.

Although various constructions have been proposed for direct electron beam recording using an electron sensitive layer, itis believed that no one has heretofore used in such a construction as the electrically conductive layer an alkali soluble material which itself is relatively nonelectrically conductive but which has homogeneously distributed therewithin finely divided particles of an electrically conductive material in a quantity sufficient to render the resulting layer electrically conductive.

Such a medium during a recording operation dissipates electrons so as to maintain electrostatic charge potential at a level which is so low as not to affect appreciably the medium or the recording electron beam. During the recording the conductive layer can be grounded.

When such a medium construction following exposure to an electron beam during a recording operation is placed in an alkaline solution, the conductive layer is more than 10 weight percent chemically completely dissolved and thereby completely removed conveniently and quickly, for example, with the aid of running water. The result is that the recorded and processed film is then optically clear (non-light absorptive) as respects its capacity to transmit light therethrough in unimaged areas (in the case of positive recordings) or in imaged areas (in the case ofnegative recordings).

It is an object of the present invention to provide a sheet-like recording medium which employs an electron sensitive layer, a base support layer and an electrically conductive layer, said conductive layer having finely divided particulate electrically conductive particles incorporated therein.

Another object of this invention is to provide an electron beam recording medium construction of the class indicated wherein the continuous portion of the conductive layer is substantially completely water soluble in alkaline aqueous solution.

Another object of this invention is to provide a method for direct electron beam recording under vacuum condi. tions and for subsequently directly reading out such recorded information by optical projection (i.e. transmission) techniques.

from an electron beam recording medium by partial techniques.

Other and further objects of this invention will become apparent to those skilled in the art from a reading of the present specification taken together with the drawings wherein:

FIGURE 1 is a vertical cross-sectional view of one embodiment of a medium construction of this invention before a recording operation;

FIGURE 2 is a view similar to FIGURE 1 but showing an alternative embodiment of the invention; and

FIGURE 3 is a diagrammatic illustration using the embodiment of FIGURE 1 showing the manner in which the conductive layer is removable from recording media of this invention.

The base support layer, the electron sensitive layer and the conductive layer will now be described. Because electron beam recording operations are generally carried out under relatively high vacuum conditions, it is desirable though not necessary to use materials in the medium constructions of this invention which are vacuum stable. It is also desirable though not necessary in making medium constructions of this invention to employ materials which have minimal residual quantities of volatilizable gases, liquids and solids associated with them because such materials when released in vacuum during electron beam recording operations can interfere with the operation of thee'lectron gun, especially its electron emission sources as those skilled in' the art will readily appreciate.

As the base support layer there is employed an optically clear, dimensionally stable material having opposed parallel anchorable faces.

For purposes of this application, the term optically clear has reference to even and high (e.g. more than 50%) light transmission in the visible region of the spectrum.

The term dimensionally stable" has reference to the fact that a material in a medium undergoes no appreciable changes in its dimensions under any of the vacuum recording, processing, storage and readout conditions to which such medium is to be subjected (i.e. such medium is not rendered inoperable by reason of dimensional changes in its support layer).

The term anchorable faces or simply anchorable has reference to the fact that the base support layer is capable of having other substances chemically or physicochemically fastened or bonded to either one or both faces thereof so as to form initially a composite, integral structure, depending upon the layers used, and their positions in a given medium construction. Thus such a base support layer may be subbed or the like before being used in a medium construction of this invention.

As those skilled in the art will appreciate, it is necessary to employ as the base support a material which is capable of having other substances anchored to either one or both faces thereof. Preferably the base support is constructed of a film forming organic polymer. A suitable thickness for the base support layer is from about 0.25 to 10 mils.

An especially preferred film support material is polyester film, such as that type technically known as polyethylene terephthalate film. Other suitable film support materials useful in the construction of sheet-like storage media of the present invention are polycarbonates, cellulose esters, polystyrenes and the like.

As the electron sensitive layer there is employed a composition capable of deeloping therein, following exposure thereof to excited electrons, internally changed regions corresponding to, or representative of, the excited electrons striking such regions. Such regions are detectable (observable) by means of the passage or transmission of light energy (i.e. energy having Wavelengths of from about 400 to 700 millimicrons) therethrough because such light energy is selectively or differentially transmitted by such regions compared to the adjacent regions.

It will be appreciated that such regions are in an imagewise pattern of either a positive or negative character, depending upon recording conditions and nature of the particular electron sensitive material used as well as upon the processing applied.

The electron sensitive composition is further characterized by the fact that when in a layered form within a medium construction of this invention, even the inherent limited power of excited electrons (i.e. those derived from a modulated electron beam) is sufiicient to enter such layer and effect the desired exposure thereof so as to produce an image-wise recording of these excited electrons. While there are many ways, as those skilled in the art will appreciate, to eifect this result, it is achieved in the present invention by controlling the uniform dis tribution of electron sensitive elements in the electron sensitive composition in such a way as to make a layer of such composition in a medium construction as thin as practicable and yet achieve maximum change in the electron sensitive layer during the beam dwell time upon a given surface area of such medium.

The term dwell time as used in this application has reference to the average time as for instance in microseconds the spot diameter formed by a moving electron beam spends in an area equal to its own.

The term element as used in this application has reference to a functional component of the electron sensitive composition which may consist of a homogeneous mixture or chemical combination of one or more chemical entities.

In general, such electron sensitive compositions are well known to those skilled in the art. For convenience and reference purposes various classes of these imaging materials are summarized in the following Table I. In this table, the term imaging process has reference to the manner in which an image is formed by a physical or chemical change in a given medium construction. Exposure is generally prolonged until the image material has undergone a change sufficient to eifect the desired recordation of information. The term development has reference to a particular chemical or physical process by which the change or alteration in image material created during exposure to electron radiation is detected and amplified. Development may (a) require a second, separate, and subsequent processing step following exposure, or (b) occur simultaneously with, or as a direct and dependent consequence, of exposure to electron radiation. The term fixing has reference to a process step subsequent to development which produces desensitization of areas in an image material to subsequent or further exposure to actinic radiation. Depending on the nature of the phenomena utilized, development and/or fixing may not be necessary, may be eliminated, or may even be accomplished simultaneously with one another.

TABLE I.FUNCTIONAL DESCRIPTIONS OF IMAGING PROCESS STEPS WITH DIFFERENT IMAGING SYSTEMS I. Imaging Process II. Development III. Fix IV. Process 1. Destroy areactant Chemical reaction forming a visibly distinct Not needed Diazo-Bruning, Ozalid} product in non-exposed areas.

2. Photodecomposition producing Heat to expand gas within softened film pro- Exposure to uniform photon Vesicular Diazo.

g'iiseiousfilpfiflucts in a thermoducing light scattering bubbles. energy. p as 10 3. Create a heat pattern (localized Heat sensitive physical or chemical change to Background is heat sensitive Thermography.

increase in temperatur produce a visibly distinct product. unless fixed.

4. Create a pattern of a chemical Transfer and chemical reaction to yield a Not needed Sympathetic ink.

reactant. visibly distinct product.

5. Generate acidic reactant Conversion of basic dye to acid form do Described herein below.

6, Producing structural rc-arrange- Photochromatic (conversion of one chemical do Photoohromic rnicroimag'e ment. species to different chemical species). PCMI)! 7. Free radical generation Synthesis of photon absorbing material Heat Wainer reaction.

8. Degradation of silver halide to free Chemical amplification of the exposed latent Chemical removal of un- Photography.

silver. image. developed silver halide.

1 U.S. Patent Nos. 2,829,976; 2,807,545; 2,755,135; 2,774,669; 2,691,587.

2 US. Patent No. 2,740,896.

British Patent No. 844,077; 844,079; 844,256; Niepce de St. Victor, Photographic News 2 (1859). V

4 Y. Hirshberg J.Ohem. Phys. 27, 758 (1957); South Africa Patent No. 61861; French Patent No. 1,272,059; Belgium Patent No. 607,355; British Patent Nos. 887,958; 88,902; 883,803; US. Patent Nos. 3,090,687; 3,038,812; 3,020,171; 2,953,454; 3,022,313.

For purposes of this invention it is generally convenient and satisfactory to employ an electron sensitive composition which when deposited in a layered form upon an inert surface to a thickness of about 2 (microns) will develop an optical density of at least one when exposed to not more than 10 electrons per square centimeter of layer surface area, When said electrons are accelerated to penetrate substantially all of the sensitive layer.

The optical density (D) of an electron sensitive layer deposited in a medium construction of'this invention is defined by the relation D=log 0 where O is the opacity. If L and I are the incident and transmitter intensities respectively the opacity is given by 1 /1. Optical clarity can be measured as the reciprocal of the opacity or 1/1 It will be appreciated that the term develop, developing or equivalent as used in this content may or may 'not involve subsequent chemical or physical processing followingia recording operation so as to produce the desired changes in an electron beam exposed, electron sensitive composition.

5 U.S. Patent No. 3,042,515, R. H. Sprague and M. Roscow, Photo Sci. 8: Eng. 8, 91 (1964); R. H. Sprague and It. L. Fitchter, ibid p. 95; U.S. Patent No. 3,102,029.

US. Patent No. 2,950,194.

7 Glafkides "Photographic Chemistry," volumes 1 and 2 published by Fountain-Press (London, 1958).

The conventional diazo processes mentioned in Table I involves production of a colored azo dye. Exposure to excited electrons of a stabilized diazonium compound destroys its ability to react with a coupler and hence produce a dye. In the unexposed areas the dye-forming reaction occurs readily upon the addition of an alkaline mate-rial (ammonia vapor) if the diazo system already contains a coupler component or both an alkaline material and coupler.

In the so-called vesicular diazo process mentioned in Table I, exposure to excited electrons decomposes a diazonium salt dispersed in a thermoplastic binder. When the medium is subsequently heated, the nitrogen produced by the decomposition expands in the softened binder producing a vesicular, light scattering image in the exposed areas.

In Example 4 of Table I selective surface absorption or selective deposition can be used to create a differential chemical pattern of an imaging system component corresponding to that on the original graphic master. If the tinctorial power of the reaction product is high, or if the transferred material is a reaction catalyst, transfer of only very small amounts of material can provide a visible image. Thus, some degree of amplification may be possible.

For some time it has been known in the arts that upon exposure of highly halogenated polymers such as polyvinyl chloride or polyvinylidene chloride to excited electrons one obtains acidic reaction products generated in the polymer matrix, directly as a result of the irradiation. If in such a polymer matrix there is incorporated the basic form of an acid-sensitive dye such as one of the commonly known indicator dyes such as phenopthalein, then, upon exposure and generation of the acid component in the matrix, a color change is produced in the irradiated areas.

Photochromic materials are well known in the photochemical art. Such materials, when exposed to excited electrons, undergo a structural rearrangement which results in the formation of a differently and usually more colored species, compared to the initial color. A wide variety of such compounds are included in the chemical class known as benzoindolinopyranospirane. The National Cash Register Company-developed photochromic imaging system utilizing this general technology for the recording of grain-free microimages can be employed in making the electron-sensitive layer in media of this invention.

The exposure to excited electrons of highly halogenated alkanes, such as carbon tetrabromide, bromoform, or chloroform produces a highly chemically reactive radical. When, for example, a substituted aromatic amine is incorporated in close proximity thereto, upon subsequent heating an image is formed. The literature discloses that Horizons, Incorporated has made practical utilization of this color forming reaction in preparation of electronsensitive compositions. These compositions, when suitably layered in combination with fluorescent composition, can be used in electron-sensitive layers in media constructions of this invention.

Example 5 of Table I utilizes a dehydrohalogenation electron-sensitive system which employs a combination of two components: an acid sensitive indicator and a highly halogenated polymer. The acid sensitive indicator is capable of changing color at pH below about 7 when the highly halogenated polymer is capable of liberating an acid component. The halogenated polymer is normally solid and has a molecular weight of at least about 1,000 and further has at least 25% of labile halogen se lected from the group consisting of chlorine and bromine. The indicator is generally homogeneously distributed throughout the halogenated polymeric binder, and is preferably dissolved therein. It may also be provided as a localized coating or be concentrated in the top surface of the polymeric binder in .a particular medium construction. Preferably the polymers are soluble in conventional organic solvents. Solubility, of course, can be adjusted to some extent by employing copolymers, a balance being achieved between halogen content and copolymer solubility. Vinylidene chloride copolymers with such monomers as the aliphatic ac-rylates (e.g. n-butyl acrylate, methyl acrylate, ethyl acrylate, hexyl acrylate, methyl methacrylate, betachloroethyl acrylate, etc.), acrylonitrile, vinyl chloride, vinyl acetate, vinyl butyrate, etc. are preferred highly halogenated polymer systems. Ethylenically unsaturated monomers with a high halogen content, such as 1,l,3,3,3-pentachloropropene-1, fluorotrichloroethylene, l,l-difluoro-2,2-dichloroethylene, tri- 'chloroethylene, etc. copolyrnerize-d with vinyl or vinylidene chloride or bromide or with aliphatic acrylates can also be employed. Halogenated aromatic polymers are considerably less effective than the halogenated aliphatic polymers, although the copolymerization of a suitable halogenated aliphatic monomer with an aromatic monomer (e.g. styrene, vinyl toluene, vinyl carbazole, etc.)

selected for its solubility characteristics is suitable.

Although the halogenated polymers are desirably deposited from solution as a film on .a surface, they may also be deposited from a latex or intimate dispersion. With those polymers which tend to decompose slowly in the presence of ordinary light and atmospheric oxygen, antioxidants and other stabilizers may be added to improve good storage life.

Since the highly halogenated polymers serve as .a relatively non-volatile source of hydrohalic acid, no other brominated or chlorinated compounds which liberate acid under electron beam exposure are required for electron beam imaging.

An electron sensitive composition for use in media of this invention can be prepared by mixing a minor amount of the acid sensitive indicator system with a solution of the highly halogenated polymer and backing. If a transparent imaging material is desired, it will be appreciated that many of the highly halogenated polymers are made more relatively light transmissive in the form of a thin film. For each equivalent weight of acid sensitive indicator from about 1 to about 1000 acid equivalents of the halogenated polymer are employed, although the ratio of these ingredients varies with the particular indicator system, and its acid sensitivity, which is employed. Other additives, e.g. plasticizers, oxidizing agents, etc. may be incorporated into the actinic radiation sensitive coating, (preferably such additives are chosen so as not to liberate acid under the actinic radiation). Additional films or coating may be provided on the actinic radiation sensitive layer to protect it from abrasion, etc., provided they are relatively transmissive to the electron beam.

With electron sensitive compositions such as just described, a color change therein is generally observed immediately after exposure to excited electrons or shortly thereafter upon subsequent exposure to air thereby providing a visible imaging record in a layer of such a composition. In some instances, when the acid sensitive indicator is reversible, as with the acid-base indicator dyes, the image can be erased by heating the electron sensitive composition to about 100 C. to 150 C. for approximately 30 seconds, the color change being probably due to the volatilization of the acid and an increase in effective pH of the electron sensitive composition. Erased electron sensitive compositions of this type can be re-used for recording with electron beams although subsequent depletion of the polymeric acid source eventually reduces the efiiciency of recording.

It is sometimes convenient to leave the indicator out of a highly halogenated polymer film initially. Then after exposure of such film to actinic radiation, the liberated acid in the imaged (exposed) areas can be subsequently developed by contacting the exposed surface of the highly halogenated polymer With the acid sensitive indicatory system. A separate development roller or bath may be used for this post development step or a second medium construction incorporating or carrying the indicator can be physically brought into contact with the exposed surface of such medium. Such a post development procedure using an acid indicator containing film can be used to prepare multiple copies.

A simple standard test procedure to assist in the selection and definition of highly halogenated polymers and indicator systems useful in such media of this invention employs ultra-violet light. The procedure is to add to a film-forming halogenated polymer 5 milligrams of Congo red A to 1.0 milliliter of a 20 weight percent solution of such polymer, in a suitable solvent such as tetrahydrofuran. This solution is then knife coated onto a cellulose acetate, polyethylene terephthalate or glass backing .to provide a dry film of 0.1 mil thickness. A sample of this dry film is placed at a suflicient distance from an ultra-violet light source to provide about 0.08 Watt per square centimeter of radiant energy of 2000 to 3000 angstroms wavelength. The sample is irradiated for a period from 2 to 30 seconds. Generation of a blue color indicates a halogenated polymer containing labile halogen useful in the electron beam recording media of this invention. The same standard test procedure is modified for selection of a suitable acid sensitive indicator by using a 20 weight percent solution of vinylidene chlorideacrylonitrile 'copolymer (90/10 mol ratio) and milligrams of the acid sensitive indicator system, a strong color change after the ultraviolet exposure indicating a useful indicator for the electron beam recording media.

An especially preferred type of electron sensitive composition comprises silver halide emulsions.

As the photographic silver halide emulsion layer for use in the present invention, one can employ virtually any silver halide emulsion since such emulsions are generally sensitive to electron beams. However, it is greatly preferred for purposes of producing sheet-like storage media of the present invention to use emulsions which are particularly useful for electron beam recording. For the purpose of constructing media of this invention it is desirable to use fine grain emulsions, that is, emulsions having an average grain size less than about 0.5 micron.

In a given medium construction the thickness of the silver halide emulsion is largely dependent upon the quantity of silver per unit of area which is to be used for recording. Typically, the layer of silver halide emulsion contains from about 5 to 50 milligrams of silver per square decimeter of surface area.

A preferred silver halide emulsion for use in medium constructions of this invention is one which has an average grain size of less than about 0.5 micron and a silverto-gel ratio of about 1 :1.

It is sometimes convenient in fabricating medium constructions of the present invention to overcoat the electron sensitive layer with a top coat, particularly when such emulsion layer constitutes the uppermost or bottom-most exposed portion in a completed medium construction. As a top coating material one can employ a thin layer of gelatin, say, one less than about 0.5 micron in thickness. Such a layer does not interfere with the development of, for example, silver halide emulsion, following a recording operation and serves to protect the recording medium against accidental abrasion and dust particles during a recording operation as well as during subsequent storage following development.

In order to achieve a good anchoring between the base support layer or material and the particular silver halide emulsion, it issometimes desirable to employ a very thin layer of a subbing composition to the surface of the base support layer before the same is coated with an electron sensitive layer. Such compositions are known and understood to those skilled in the art. Convention subbing agents for silver halide emulsions, for example, are listed in Glafkides Photographic Chemistry, Volume I, pages As the removable conductive layer one employs a relatively non-conductive organic polymeric material which has incorporated therein sufiicient quantities of finely divided particulate electrically conductive material to render the resulting composition electrically conductive.

For purposes of this electrically conductive composition one employs conductive carbon particles, metal particles and the like. These particles range in sizes from about 0.1 to 2 microns in average maximum cross-sectional dimension.

As the non-conductive organic polymeric material one can employ virtually any alkali soluble polymeric material. One such material comprises the so-called Gantrez resins, for example, Gantrez AN, which is a product of General Aniline and Film Corporation and which is a 1:1 interpolymer of methyl vinyl ether and maleic anhydride. Other suitable types of polymers include alkali soluble polymers, methyl vinyl ether/maleic anhydride (MVE/ MA), half normal butyl ester of MVE/ MA, half isobutyl ester of MVE/ MA, half ethyl esters of MVE/ MA styrene/maleic anhydride (S/MA), S/MA half esters, and their partial esters.

In general, the loading of conductive particulate material in a resin composition is such that the resulting electrically conductive composition when in layered form has a resistivity of not more than about ohms per square 5 and preferably not more than about 10 ohms per square as measured in a vacuum of about 10 mm. Hg. Preferably a layer of such conductive material used in the construction of a recording medium of this invention has a thickness less than about 0.5 mil and more preferably in the range of from about 1 to 4 microns.

The conductive layer is usually used in a medium construction over a subbing layer to facilitate dry adhesion of the conductive layer to the remainder of the medium construction during handling and recording operations. In general, it is suitable to have the conductive layer adhered to the remainder of the film construction to an extent such that an equivalent peel force of at least 10 grams. For the purposes of this invention peel force is measured in the same manner as the 180 adhesive bond strength test described in A.S.T.M. test procedure number D-1000. It will be appreciated that such adherence or bonding may be achieved by the manner in which a given medium construction of this invention is manufactured, as is more particularly described below. In a layer is so positioned as to comprise an outer face there- (a) the optical clarity of the base support layer, and

(b) the image quality of information developed in the electron sensitive layer.

During this contacting the following variables are taken into consideration:

(1) Temp'eratwre.-As those skilled in the art will appreciate, temperature extremes and extreme temperature changes are undesirable. For example, in the case of silver halide emulsions coating development the temperature of the aqueous alkali removal bath should be equal to the subsequent processing solutions, say about 68 F. In general, a temperature in the range of 55 to 75 F. is satisfactory.

(2) Solution concentration.A preferred range of pH values is from about 7.5 to 10 (e.g. equivalent to about an 0.01 N to 0.1 N NaOH solution).

(3) Time in solutionr-In general, it is preferred to have a complete dissolution of the conductive layer take place in less than 1 minute, and, more preferably, in less than about 30 seconds.

The following Table 11 gives an indication of the relationship between the thickness of the conductive layer, the concentration of the alkali solution, the time in the 6O alkali, and the time to wash off the conductive layer.

TABLE II Conductive Normality of Layer NaOH Solution Time in Alkali Time in Wash Thickness 7 see. Not completely removed. 2 sec. 2 sec. 3 see. 3 sec. 5 see.

medium construction of the invention, the conductive It will be appreciated that in a given medium construction of this invention, the total thickness of, and the interrelationship between layers thereon is such that, immediately after a recording operation, the potential in volts remaining E, the charge of coulombs remaining q, and the distance d between adjacent faces of said electron sensitive layer. and said removable conductive layer is such that where k is a proportionality constant characteristic of a given medium construction under a given set of recording parameters. If E is too large, then there are the possibilities of (a) excessive arcing between the electron sensitive layer with the result that fogging of the recorded image can occur, (b) the recording modulated electron beam is deflected in adjacent areas so that accurate positioning of the beam with respect to the medium is lost in recording, and (c) the medium is physically attracted by electrostatic forces to surrounding or adjoining surfaces to such an extent that the medium becomes difficult to handle (i.e. transport) in the recording equipment.

Such layer interrelationship and medium total thickness considerations depend not only upon the nature of the starting materials but also upon the manner in which a particular medium construction is assembled, aside from recording, processing, and readout conditions.

Usually the layers are kept distinct one from the other in a medium construction. While adjoining layers need bear no special relationship to one another, it will be appreciated the electron sensitive layer should be so located with relationship to the exterior surface of a given medium construction so as to facilitate any necessary or desirable development of that layer following a recording operation. It is preferred to keep the electron sensitive layer as close as possible, consistent with the type of construction desired and with the materials of construction'being used, to the conductive layer so as to keep at as small as possible relative to q in a given construction. Preferred medium constructions in general are flexible and thin so as to have total thicknesses of the same order of magnitude commonly associated with conventional photographic film and magnetic tapes so as to permit the use of transport mechanisms similar to those used in magnetic tape recorders and motion picture equipment and handling procedures generally.

. Anespecially preferred class of medium constructions within the teachings of the present invention are those capable of recording information in a high density manner, that is to say, capable of recording information at a bit density greater than about 10 bits of information per square centimeter of.surface area.

Media constructions of this invention can be prepared by any convenient, conventional procedure. For example, to make a construction of FIGURE 1, one can begin with a preformedoptically clear base support layer. Then one or both faces of such layer can be subbed and coated in turn with a layer of electron sensitive composition or the base support can be purchased already subbed on one or both sides. Finally, the removable conductive layer can be coated upon the opposed face of the base support layer. Except for the conductive layer, the various coatings can be applied as solutions or slurries of composition in a volatile liquid using knife, roll, or similar coating procedures. After application, a coating may be dried before another layer is coated.

. Electron sensitive compositions do not constitute in themselves any part of this invention but rather are known to the art, therefore, no detailed explanation or description of such treatments is considered necessary or desirable herein beyond that already given above in reference to Table I.

To use a medium construction of this invention, one exposes same to a modulated, electron beam under vacuum conditions making sure that the conductive layer is grounded during such beam exposure. As the techniques of electron beam recording are well worked out and form no part of this invention, detailed explanation thereof is not given herein. However, for illustrative purposes, it is noted that a typical conventional electron beam recording operation may utilize an electron beam characterized by having a beam diameter of from about 1 to 25 microns, a voltage of from about 10 to 30 kv., a current flow of from about 10- to 10* amps and adapted to scan a target area at a rate such that the dwell time is from about 10 to 10- seconds. Vacuum pressures commonly range from 10- to 10- torr.

After such a recording operation the conductive layer is removed from the so-exposed medium construction by dissolution. Using conditions as explained above, any necessary or desirable chemical or physical treatment of the electron sensitive layer is carried out, as, for example, to develop a latent image when this layer is a silver halide emulsion. As such chemical or physical treatment is a characteristic associated with the particular type or electron sensitive composition employed in any given medium construction, and as such chemical or physical treatment involves procedures well known to those of ordinary skill in the art and form no part of the present invention, they are not described in detail herein.

For example, the conductive particulate layer is removed by immersing the medium in 0.01 normal sodium hydroxide solution at 68 F. for 5 seconds and then positioned under a jet stream of Water at 68 F. thereby dissociating the layer and washing it away.

After processing the resulting medium can be read out by optical projection (transmission) techniques. For example, the medium can be then placed in a conventional photographic projector and projected on a white surface.

Referring to the FIGURE 1 of the drawings there is seen a medium construction having a base support layer 10 which has an anchorable face 11 achieved by subbing. The subbed face 11 is coated with an electron sensitive layer 12, for example, a silver halide emulsion. The other face of base support layer 10 is coated with a removable conductive layer 13. Observe that there is positioned between layer 13 and layer 10 a subbing layer 14 which serves to facilitate dry anchorage between layer 13 and layer 10.

In FIGURE 2 is shown another embodiment having a base support layer 16 which is subbed or coated on one of its faces with a subbing layer 17. The layer 17 is in turn coated with a layer 18 of electron sensitive material, for example, silver halide emulsion. Finally, the layer 18 is coated with a removable conductive layer 19.

In FIGURE 3 is illustrated the manner in which, for example, the conductive layer 13 of the construction of FIGURE 1 is removed. When such a construction is placed in an aqueous alkaline medium 21, the layer 13 disintegrates owing to the dissolution of the binder. The result is that the conductive layer 13 is substantially completely removed without affecting a recorded image in layer 12 or the optical clarity of layer 10.

The invention is further illustrated by reference to the following specific examples. Unless otherwise indicated, the term parts as used in these examples refers to parts by weight.

EXAMPLE 1 (a) Removable conductive layer: Application to base support layer A dissolvable binder for the carbon black conductive dispersion is prepared in the following manner:

Parts by weight Poly methyl vinyl ether/maleic anhydride 10 Isobutyl alcohol The methyl vinyl ether/maleic anhydride 1:1 copolymer designated MVE/MA (commercially available, for example, as Type Gantrez AN-1l9 from General Aniline procedure is used:

Parts 15% solids solution of the half isobutyl ester of MVE/MA in isobutyl alcohol 1720 Conductive carbon black 125 Glycerine 27 Surface active agent, Triton X-100 1 The solution of the half isobutyl ester of MVE/MA is added to a steel container together with the glycerine and surface active agent (Type Triton X-lOO, Rohm and Haas Co.). While mixing the solution with an Eppenbach type of homomixer, manufactured by Gifford Wood Company in Hudson, New York, the carbon black is slowly added. After the addition of the conductive carbon black Type Vulcan XC-72, produced by Cabot Corporation, the disperson is allowed to mix an additional 15 minutes. Finally, an additional 780 parts of isobutyl alcohol is blended in by stirring. The pigment-to-binder ratio of the above dispersion is about 1:2.

This dispersion is then coated on one side of a flexible, transparent film of polyethylene terephthalate (available as Type A, 500 gauge, Mylar from E. I du Pont de Nemours & Company, Inc.) which is provided with a substratum on both sides to make coatings from aqueous or alcoholic solutions adhere to it on both sides.

The substratum is prepared according to the teachings of British Patent No. 552,085 (1943).

The conductive coating is accomplished by conventional rotogravure methods and gives a dry, tough film of about 2.5 microns in thickness and a resistivity of about 300 ohms per square.

(b) Silver halide emulsion layer: Formulation and application A photographic emulsion and supercoating solution are prepared and coated on the side opposite the conductive coating.

The silver halide emulsion is prepared according to principles described in Glafkides Photographic Chemistry, Volume I, pages 341-353. The resulting emulsion contains 3.5% silver, a silver-to-gelatin ratio of 1:1 and a mol ratio between silver bromide and silver chloride of 12 to 88. The emulsion contains all the necessary coating finals known to those skilled in the art, and as described in Glafkides Photographic Chemistry, volume I, chapter 21, pages 369-389.

The coated emulsion layer after coating is approximately 2 /2 microns thick and contains approximately 25 milligrams of silver per square decimeter. The emulsion preparation, coating and subsequent steps are carried out under red-type illumination only. The emulsion supercoated with a protective gelatin layer of about 0.5 micron thickness. Layers of this type and their preparation are described in Glafkides Photographic Chemistry, volume I, paragraph 359, pages 386 and 387. This film construction is now slit into film strips of 16 millimeter width and perforated.

(c) Use of medium construction The medium is now used for exposure by electron beams as follows:

The medium is mounted into a 16 millimeter motor driven sprocket drive tape transport mechanism and guided under an electron beaam in a vacuum chamber under a vacuum of about 5 10- mm. Hg. The axis of rotation of the sprocket is parallel to the direction of the 12 deflection of the electron beam so that the plane of film movement is effectively perpendicular to the direction of deflection. Film or tape speed is about 9 inches per second.

A conventional television-type deflection is used to defleet the electron beam. The horizontal deflection is accomplished by driving the deflection coil on the electron gun with a 15,750 cycles per second sawtooth current. The sawtooth has a scan period of about 53.5 microseconds and a retrace period of about 10 microseconds. The resultant horizontal deflection of the electron beam is set for about 1 centimeter width at the surface of the medium. 7

The electron beam is about 10 microns in diameter at the surface of the medium and has an acceleration of about 15 kilovolts. The beam current is intensity modulated by applying a modulating voltage at the gun grid. The intensity modulation of the beam corresponds to the information to be recorded. The peak beam current during such modulation is about 0.1 microampere.

The medium and electron gun are mounted in a vacuum chamber held at about 5 X 10* mm. Hg pressure.

The recording takes place by simultaneously moving the film or tape and deflecting, and modulating the electron beam so that a scanned line-like latent image pattern of the information results.

Afterrecording and removal from the vacuum chamber the exposed medium is processed. The conductive particulate layer is removed by immersing the medium in 0.01 normal sodium hydroxide solution at 68 F. for five seconds and then positioned under a jet stream of water at 68 F., thereby dissociating the layer and washing it way. The recorded medium is then dried.

For retrieval (readout) of the recorded information the film medium is positioned in a 16 millimeter movie projector and projected by the light source against a white surface.

High fidelity reproduction of recorded information is achieved.

EXAMPLE 2 The same procedures and coating formulations are used in Example 1 except these materials are coated on a base support of cellulose triacetate commercially available from Eastman Kodak Company to make a medium construction of the invention. After exposure and processing under conditions like those described in Example 1, high fidelity optical readout is obtained as in Exam- .ple 1.

EXAMPLE 3 The same electron sensitive material and base support are used as in Example 1.

The following conductive dispersion is formulated:

. Parts MVE/MA poly methyl vinyl ether maleic anhydride 8.8

n-Butyl alcohol 91.

EXAMPLE 4 To prepare a conductive coating which may be removed by immersion in water, the following procedure is employed:

To 20 grams of a solution in anhydrous ethanol containing 50% solids of 70:30 weight .ratio copolymer of N-vinyl-2-pyrrolidone and vinyl acetate supplied as PVP/VA Type I-735 by the Antara Chemical Division of General Aniline and'Film Corporation, New York 14, New York, is added 30 grams of conductive silver powder, electronic grade V-9, supplied by the E. I. du Pont de Nemours & Co., Wilmington, Del. After stirring the mixture to achieve a uniform dispersion, it is coated by means of a knife-type stripe coater onto a 5 mil thick backingiof cellulose triacetate film, supplied as Kodapak IV, F401 (now designated Kodacel TA401) by the Plastic Sheeting Division, Eastman Chemical Products, Inc., Kingsport, Tenn. The coating is dried at 200 F. for two minutes and found to be 1.3 mils thick. The coating is observed to have good adhesion to the film backing'and resists removal when subjected to the pressure-sensitive adhesive tape test. The coating has a resistivity of l-20 ohms per square. After immersion in water for 15 seconds it is found that the coating dissolved to such an extent that it is readily removed from the backing by a light brushing action. When this resulting construction is coated with a silver halide emulsion layer and used according to the teachings of Example 1, high fidelity reproduction of recorded information is achieved.

EXAMPLE A sample of fabric, designated Pluton-H, a trademark of the 3M Co., which was prepared by the 3M Electrical Products Laboratory is employed. The sample is a 20 mil thick fabric consisting of a carbon-type fiber which is made by a catalytic process at high temperature in an inert atmosphere to cause the conversion of the fiber material to a carbonized structure. The resistance of the Pluton-H fabric is found to be about ohms per square. To prepare a coatable dispersion of the Pluton-H fiber, the fabric is first ground to a small particle size by means of three passes through a tight setting on the rolls of a rubber mill. Examination of the ground Pluton-H material shows it to consist chiefly of fine particles of less than 0.01 millimeter with a small amount of short fibers ranging from 0.5 to 1 millimeter in length.

In Table III is shown the compositions of the dispersions A through E and resistance measurements for the coatings prepared by knife coating the dispersions onto a 1 mil backing of polyester film. The polyester film was primed with a coating of a polyvinylidene chloride type polymer available as Saran F-220 (Dow Chemical Co.) The resistance measurements were made on the air dried coatings. Dispersions A, B and D were prepared by stirring the conductive powder into a solids solution of the partial ester ofisobutyl alcohol with a copolymer of maleic anhydride and methyl vinyl ether in isobutyl alcohol solvent.

Dispersion C was obtained by a further grinding of dispersion B by means of the action of a Quickie Mill using inch burnishing steel balls. Dispersion E was obtained by mixing equal volumes of dispersion C with dispersion D.

All coatings of the conductive powder in the binder were readily washed off the backing by a 15 second soak in one normal sodium hydroxide followed by a water rinse.

TABLE III.-DISPERSIONS OF CONDUCTIVE POWDER IN A SOLUBLE BINDER 1 Polymer binder was the isobutyl partial ester of Gantrez AN-119 (General Aniline & Film Corp, New York 14, New York).

2 Carbon black was Vulcan XC-72 (Cabot Corp., Boston, Mass).

8 Resistance reading over 1 megohm per square was recorded as High.

When this resulting construction is coated with a silver halide emulsion layer and used according to the teachings of Example 1, high fidelity reproduction of recorded information is achieved.

We claim:

1. In a method for direct electron beam recording of information in a sheet-like recording medium adapted for readout of pre-recorded information by optical projection, said medium containing a base support layer, an electron sensitive composition layer, and a conductive layer positioned on one face of said medium and composed of an alkali soluble organic polymeric binder and conductive particles distributed homogeneously therein, the improvement which comprises the steps of:

(a) exposing under vacuum one surface of such a medium to an electron beam modulated with information to be recorded while simultaneously grounding the conductive layer of such medium, said beam having an associated energy and relative motion adapted for recording such modulation in the electron sensitive composition layer of such medium, and

(b) thereafter contacting said conductive layer with an aqueous alkaline liquid for a time sufficient to dissolve and thereby remove such layer from such medium.

2. A sheet-like storage medium adapted to (a) develop therein an image pattern corresponding to information associated with a modulated electron beam when such a beam scans one face thereof during a recording operation,

(b) dissipate electrons during such an electron beam scanning operation, said dissipation being at a rate sufiicient to maintain the negative charge associated therewith in said medium at a level which substantially does not adversely affect the recorded image,

(c) be processed after such recording operation and before readout by conventional optical transmission techniques so that the imaged areas selectively modulate transmitted light,

said medium comprising in combination (a') an optically clear, dimensionally stable, base support layer having opposed parallel anchorable faces,

(b') a layer of electron sensitive composition on one face of said base support layer, said composition being characterized by the chemical capacity to develop an optical density of at least one when exposed to not more than 10 electrons per square centimeter of layer surface area, when said electrons are accelerated to penetrate substantially all of the sensitive layer,

(c') an electrically conductive layer positioned either over said layer of electron sensitive composition or over said base support layer, said conductive layer (1) consisting of an organic polymeric binder having dispersed therein finely divided conductive particulate materials, and

(2) said binder being characterized by having the capacity to become water soluble when treated in aqueous alkaline medium, thereby to affect removal of said conductive layer from the remainder of said medium without appreciably afiecting at the time of removal:

(a") the optical clarity of the base support layer, and

(b") the image quality of information developed in said electron sensitive layer.

3. The medium of claim 2 wherein in said conductive layer the quantity and distribution of said particles are such as to impart to said composition when in layered form a resistivity of not more than about 10 ohms per square in a vacuum of about 10'- mm. Hg.

4. The medium of claim 2 wherein said base support layer is a polyester film.

'5. The medium of claim 2 wherein said base support layer is a cellulose ester film.

6. The medium of claim 2 wherein said electron senticulate materials of said conductive layer are metal sitive composition layer is a silver halide emulsion. particles.

7. The medium of claim 2 wherein the organic po- References Cited lymeric binder in said conductive layer is a polymer of UNITED STATES PATENTS methylvinyl ether and maleic anhydride. 5

8. The medium of claim 2 wherein the organic 3: 2:2 333 polymeric bmder 1n sald COIIdUClIIVe layer 18 a polymer 3,196,011 7/1965 Gunther et a1. 961

of N-vinyl-Z-pyrrolidone and vinyl acetate.

9. The medium of claim 2 wherein theconductive pa-rticulate materials of said conductive layer are carbon 10 RICHARD WILKINSON Pnmary Emmmer' particles. J. W. HARTARY, Assistant Examiner.

10. The medium of claim 2 wherein the conductive par- 

1. IN METHOD FOR DIRECT ELECTRON BEAM RECORDING OF INFORMATION IN A SHEET-LIKE RECORDING MEDIUM ADAPTED FOR READOUT OF PRE-RECORDED INFORMATION BY OPTICAL PROJECTION, SAID MEDIUM CONTAINING A BASE SUPPORT LAYER, AN ELECTRON SENSTIVE COMPOSITION LAYER AND A CONDUCTIVE LAYER POSITIONED ON ONE FACE OF SAID MEDIUM AND COMPOSED OF AN ALKALI SOLUBLE ORGANIC POLYMERIC BINDER AND CONDUCTIVE PARTICLES DISTRIBUTED HOMOGENEOUSLY THEREIN, THE IMPROVEMENT WHICH COMPRISE THE STEPS OF: (A) EXPOSING UNDER VACUUM ONE SURFACE OF SUCH A MEDIUM TO AN ELECTRON BEAMS MODULATED WITH INFORMATION TO BE RECORDED WHILE SIMULTANEOUSLY GROUDING THE CONDUCTIVE LAYER OF SUCH MEDIUM, SAID BEAM HAVING AN ASSOCIATED ENERGY AND RELATIVE MOTION ADAPTED FOR RECORDING SUCH MODULATION IN THE ELECTRON SENSITIVE COMPOSITION LAYER OF SUCH MEDIUM, AND (B) THEREAFTER CONTACTING SAID CONDUCTIVE LAYER WITH AN AQUEOUS ALKALINE LIQUID FOR A TIME SUFFICIENT TO DISSOLVE AND THEREBY REMOVE SUCH LAYER FROM SUCH MEDIUM. 